This research program involves the study of animal models of hepatitis B virus. Two such viruses have been identified during the course of this work and one has been extensively characterized. The woodchuck hepatitis virus (WHV) appears to be a close model for the virology and pathogenesis of hepatitis B, and is being used to develop a system for studying virus replication in cultured primary hepatocytes. A second HBV-like virus of Pekin ducks is being characterized further as to its distribution and pathogenecity, and will also be used for the in vitro study of virus-infected cells.